import java.util.Scanner;

public class XiaoMing {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);

        int price = scanner.nextInt();
        int day = 0;
        int totalMoney = 0;

        while(totalMoney<price){
            day++;
            totalMoney+=day;
        }
        System.out.println(day);

        scanner.close();
    }
}